The present invention relates generally to a seat belt tensioning mechanism for motor vehicles and, more particularly, to a vehicle-sensitive seat belt tensioning mechanism operable to automatically retract the seat belt buckle for tensioning the seat belt against the seat occupant in response to the vehicle being subjected to a deceleration force exceeding a predetermined critical value.
Modernly, virtually all motor vehicles are equipped with some type of passenger restraint system for physically restraining the seat occupant when the vehicle is subjected to high rates of deceleration which may occur, for example, during heavy braking or a collision. As is known, the most common type of passenger restraint system is a seat belt system having at least one of a lap belt and a shoulder belt, or a combination thereof, that can be withdrawn from a retractor device for latched engagement with an anchored buckle member. Typically, the retractor device includes a locking mechanisms for inhibiting withdrawal of the seat belt when the vehicle is subjected to deceleration forces exceeding the predetermined critical level, thereby restraining the vehicle occupant.
One type of seat belt retractor, commonly referred to as an "emergency locking retractor" (ELR), permits the seat belt to be freely withdrawn from the retractor in response to movement of the seat occupant during normal operating circumstances, thereby providing increased comfort and freedom of movement for the seat occupant. In addition, many seat belt retractors are also frequently equipped with a tension relief device or so-called "comfort" mechanism which prevents the retractor from constantly exerting a tensioning force on the belt webbing which tends to be uncomfortable and annoying to the seat occupant. Typically, the "slack" generated by the comfort mechanism can be cancelled by withdrawing a relatively short length of the belt from the retractor.
While seat belt retractors generally perform satisfactorily, the existence of an excessive amount of "slack" in the seat belt (i.e., such as when the seat occupant is sitting forward in the seat) may permit the seat occupant to be thrown forward and collide with onboard structures during the occurrence of such a deceleration force being exerted on the vehicle. To prevent such secondary impacts, the protection which is afforded by conventional seat belt systems can be further enhanced by the use of a belt tensioning mechanism. In general, belt tensioning mechanisms function to remove slack from the seat belt immediately after occurrence of the deceleration force such that the seat occupant is physically restrained within the seat before being thrown forward due to the inertia of the collision.
Conventional seat belt tensioning mechanisms are typically incorporated into the seat belt retractor and operate to retract the seat belt into the retractor upon detection of the deceleration forces. Alternatively, it is also known to use a separate tensioning mechanism which is operably coupled to the buckle member for causing retractive movement of the buckle member such that existing "slack" in the seat belt is removed. In either case, most commercially available belt tensioning mechanisms are complex mechanical or electro-mechanical systems which are generally quite expensive and difficult to install. Furthermore, some belt tensioning mechanisms are sub-assemblies of the seat and therefore are considered to be "seat-sensitive" systems (i.e., function to detect movements of the seat).
In view of the foregoing, a need exists to provide an improved belt tensioning mechanism having a substantially simplified structure and operation. In this regard, the belt tensioning mechanism of the present invention is constructed and arranged to minimize the number and complexity of mechanical parts, decrease the reaction time required to sense the deceleration and tighten the seat belt, while increasing the overall effectiveness of the seat belt restraint system.
It is therefore an object of the present invention to provide a mechanical "buckle-type" belt tensioning mechanism that is responsive to vehicle deceleration levels above a predetermined critical value for retracting the buckle member so as to apply a "tensioning" load on the seat belt for minimizing forward excursions of the seat occupant.
It is a further object of the present invention to provide a mechanical "buckle-type" belt tensioning mechanism having a unique triggering arrangement for actuating a pre-loaded drive mechanism in response to detection of the deceleration forces. According to the present invention, the above objects are accomplished by providing a "vehicle-sensitive" belt tensioning mechanism having inertia sensing means for sensing the magnitude of a vehicle deceleration, a pre-loaded drive mechanism operable for rotatably driving a reel member, coupling means for coupling the buckle member to the reel member, triggering means for actuating the drive mechanism in response to the inertia sensing means, and locking means for lockingly retaining the belt buckle member in a retracted condition following actuation of the drive mechanism.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and appended claims, taken in conjunction with the accompanying drawings.